This invention relates generally to the field of video image projection systems. More particularly, the invention relates to such projection systems utilizing high power cathode ray tubes in which substantial energy is applied by the cathode ray tube to its faceplate.
Video image projection systems have become increasingly popular, both in relatively low power units for use in home applications with larage-screen televisions and in high power applications for use in theater applications and the like. In this latter, higher power type the ultimate performance is frequently limited by the power that may be utilized by the cathode ray tube. Such limitations have frequently manifested themselves in several performance limitations. The application of very high power levels to the phosphors on the interior side of the faceplate of the cathode ray tube may, in conventional equipment, cause excessive heating of that faceplate, thus creating significant thermal stresses between the heated faceplate and the relatively unheated bowl of the tube that joins to the faceplate. Such thermal stresses have manifested themselves in cracking of the faceplates and bowls due to these thermal stresses, thus reducing the useful life of the cathode ray tubes themselves. Additionally, the problems have also manifested themselves in the blurring, or "blooming", of the image when extremely high power levels are applied by the power supply to the electron gun used in the cathode ray tube. To reduce the problem caused by the thermal stresses, it has become a conventional practice to provide liquid cooling to the faceplate of the cathode ray tubes, as described in my previous U.S. Pat. No. 4,151,554. However, even this provision of liquid cooling was insufficient to eliminate the problem of excessive thermal stresses, so that the cathode ray tubes utilized in such application have frequently failed prematurely as a result of cracking of the faceplate.
I have discovered that one of the primary problems with the prior liquid cooling arrangement for this apparatus has related to the still substantial temperature differential between the heated faceplate and the unheated adjacent bowl portion of the tube.